In recent years, development of liquid crystal display devices has been greatly advancing, and their display performance has been greatly improving. However, further improvements in display performance are demanded of some product forms that use liquid crystal display devices. In particular, practical realization of a liquid crystal display device which is capable of performing display with high luminance and high definition as well as providing excellent viewing angle characteristics as compared with conventional devices is demanded.
In general, liquid crystal display devices include a pair of substrates and a liquid crystal layer interposed between these substrates. For example, in active matrix display devices which use thin film transistors, one of the substrates is provided with pixel electrodes for applying voltages to the liquid crystal layer and thin film transistors provided as switching elements corresponding to the respective pixels, and the other substrate is provided with a counter electrode. Surfaces of the substrates which are in contact with the liquid crystal layer are covered with alignment films for regulating the alignment of liquid crystal molecules.
A known technique for improving the viewing angle characteristics of such liquid crystal display devices is to provide, in one or both of the substrates between which the liquid crystal layer is held, a structure for regulating the liquid crystal alignment (hereinafter, simply “alignment regulating structure”) such that a plurality of domains that have different alignments of liquid crystal molecules are formed in one pixel (alignment division). For example, a structure in which liquid crystal molecules are oriented vertically to the substrates and a slit provided in the pixel electrode made of a transparent conductive material (for example, ITO; Indium Tin Oxide) and a protrusion (rib) provided in the counter substrate regulate the alignment of liquid crystal molecules (MVA mode; Multi-domain Vertical Alignment), and a structure in which slits provided in the pixel electrode and the counter electrode are used to incline liquid crystal molecules according to an electric field extending in an oblique direction or “oblique electric field” (PVA mode; Patterned-ITO Vertical Alignment) have been proposed.
However, in the PVA mode and MVA mode liquid crystal display devices, it is necessary to form a complicated alignment control structure, such as slit or rib, so as to be incorporated in a pixel. Therefore, in terms of processing accuracy, transmittance of light, or any other factor, improvements in the viewing angle characteristics and display brightness are limited.
On the other hand, a technique for improving the viewing angle characteristics by a simpler structure, without forming a complicated alignment control structure, has been proposed. For example, Patent Document 1 proposes that a plurality of liquid crystal droplets (liquid crystal regions) are formed in the liquid crystal layer, and this is utilized for enlarging the viewing angle.
Patent Document 1 discloses a polymer dispersed liquid crystal display device that uses a liquid crystal layer in which liquid crystal droplets are dispersed in a resin (FIG. 61 of Patent Document 1). Outside the pair of substrates between which the liquid crystal layer is held, a pair of linear polarizers are provided in a crossed Nicols arrangement, and λ/4 plates are provided between the respective linear polarizers and the liquid crystal layer. In this liquid crystal display device, in the absence of an applied voltage across the liquid crystal layer, the liquid crystal molecules in the liquid crystal droplets are radially oriented (FIG. 63 of Patent Document 1), resulting in a white display state. When a voltage is applied across the liquid crystal layer, the liquid crystal molecules in the respective liquid crystal droplets are oriented vertical to the substrate surfaces, resulting in a black display state.
Thus, a liquid crystal display device can be obtained which can be manufactured by a convenient process at a low cost as compared with the technique of forming a rib in a substrate and the technique of forming a slit in an electrode, and which has improved viewing angle characteristics.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2002-303869
Patent Document 2: Japanese Laid-Open Patent Publication No. 7-120728
Patent Document 3: Japanese Laid-Open Patent Publication No. 2000-206515
Patent Document 4: Japanese Laid-Open Patent Publication No. 5-61025